(1) Field of the Invention
The present invention generally relates to evaporative fuel control canisters, and more particularly to an evaporative fuel control canister containing an absorbent which swells by absorbing liquid fuel.
(2) Description of the Related Art
During a supply of fuel to a fuel tank in a vehicle equipped with an internal combustion engine, a large amount of fuel vapor evaporates. Even while the vehicle is traveling or stopping, some fuel in the fuel tank or a carburetor float chamber evaporates. In order to prevent leakage of fuel vapor to the atmosphere, an evaporative fuel control canister (hereafter simply referred to as a canister) filled with an absorbent is connected to the fuel tank.
A conventional canister is disclosed in Japanese Laid-Open Patent Publication No. 62-265460 (which corresponds to U.S. Patent Application S.N. 851,547 filed on Apr. 14, 1986). The canister disclosed in this document has an activated charcoal layer having an opening formed at an upper portion thereof and exposed to the atmosphere, and a liquid separate chamber at a lower portion thereof. A vapor passage and a purge passage are provided so that they penetrate the activated charcoal layer and are connected to the liquid separate chamber.
Another conventional canister is disclosed in Japanese Laid-Open Patent Publication No. 1-227861. The canister disclosed in this document has a liquid separate chamber at an upper portion thereof and an activated charcoal layer at a lower portion thereof. The liquid separate chamber is filled with particles of an organic polymer compound which serves as an absorbent liquid fuel.
However, conventional canisters as described above have a disadvantage in that the activated charcoal layer may be wet in a state where a certain amount of liquid fuel is collected in the liquid separate chamber by vibration of the vehicle, etc. Since the liquid fuel contains a large number of constituents having high boiling points, the activated charcoal degrades greatly when it comes into contact with the liquid fuel.
In order to eliminate the above-mentioned problem, it may be possible to fill the liquid separate chamber disclosed in Japanese Laid-Open Patent Publication No. 62-265460 with the absorbent disclosed in Japanese Laid-Open Patent Publication No. 1-227861. However, since the absorbent swells (increases in volume) by absorbing liquid fuel, the passage resistance of the absorbent in the liquid separate chamber increases due to liquid fuel absorption, so that the normal purging function cannot be obtained.